Handsome Audio Zulu/Passive Distortion Theory

[MrG]

Hey all,

I have been scouring for ways to passively drive/saturate my large collection of mixing transformers and this box popped into my mind. I have a Zulu and it sounds great. It has definite distortion and saturation capabilities even though it is entirely passive.

Can anyone shed any light on theories/techniques to get this kind of distortion passively? I’m open to any concepts as long as they’re passive.

Thanks much,
Mark

 

[scott2000]

I googled passive distortion and saw some things??...

I think some guitar stuff ...????
You could always peek at your thing if you're curious...... ???

Very cool....That thing seems to have some good reviews...Never heard of it.....

 

[MrG]

Yea I’ve found some stuff too but nothing too useful I don’t think.

What about introducing feedback from the secondary to the primary of the trafo?

MG

 

[ruffrecords]

I think the Zulu is basically a small cored transformer designed to saturate at modestly high levels. I am sure CJ could come up with one.

Cheers

Ian

 

[merlin]

I'm thinking it also contains a diode clipper, with pots to adjust the series and shunt resistances. Also probably series diodes to simulate crossover distortion, wih pots to blend it in or out.

 

[ruffrecords]

I'm thinking it also contains a diode clipper, with pots to adjust the series and shunt resistances. Also probably series diodes to simulate crossover distortion, wih pots to blend it in or out.

I think you are right. ISTR the thing is potted.

Cheers

Ian

 

[Monte McGuire]

If you add a DC supply, you could use that to DC bias the core by passing DC through a winding and provide even order distortion. I suppose you could do that with a core with a hole drilled in it and a movable slug that passes a permanent magnet into or out of the core to bias it without using DC, but it'd be somewhat complicated to machine that (at least for me).

The difference is that a small core will provide symmetric distortion, while DC bias will provide asymmetric distortion, which should sound different.

 

[MrG]

Hey all,

Thank you very much for these insights.

I'm thinking it also contains a diode clipper, with pots to adjust the series and shunt resistances. Also probably series diodes to simulate crossover distortion, wih pots to blend it in or out.

I wondered about the diode clipper but, though I’ve never heard one, people seem pretty critcal of the resulting sonics, a la Black Ice. Is there a method or component choice which is decidedly more pro/useful sounding? Maybe I’ll try it out and see what I hear.

I think the Zulu is basically a small cored transformer designed to saturate at modestly high levels. I am sure CJ could come up with one.

Cheers

Ian

Small core like a Beyer peanut, for example? I have some of those that I could play with. Thing is, and forgive me if you’re well aware, you can turn knobs on the box and it takes the signal from a little harmonically saturated to full on warm distortion. I’m wondering how one can alter the headroom or distortion characteristics of a transformer (small core or otherwise) with a circuit... Or are you all suggesting that the only elements of this which noticeable add distortion are diode clippers?

If you add a DC supply, you could use that to DC bias the core by passing DC through a winding and provide even order distortion. I suppose you could do that with a core with a hole drilled in it and a movable slug that passes a permanent magnet into or out of the core to bias it without using DC, but it'd be somewhat complicated to machine that (at least for me).

The difference is that a small core will provide symmetric distortion, while DC bias will provide asymmetric distortion, which should sound different.

I’m doing my best to stay away from active circuits. Full disclosure, because I am still learning and haven’t done much with active/power supplied units. If there’s a simple answer to a DC supply that you’d recommend which wouldn’t change my whole layout due to safety concerns, etc.?

I think you are right. ISTR the thing is potted.

Cheers

Ian

Fun stuff. So does this literally mean it could not be fixed by the manufacturer? I’m not 100% on the effects of potted, but I remember you saying something about not being able to replace caps in a Fat Box DI.

Thanks so much all and I look forward to hearing your further insights.

Mark

 

[merlin]

I wondered about the diode clipper but, though I’ve never heard one, people seem pretty critcal of the resulting sonics, a la Black Ice. Is there a method or component choice which is decidedly more pro/useful sounding? Maybe I’ll try it out and see what I hear.

I don't know what Black Ice is*, but a simple pair of clipping diodes can be harsh and fatiguing it's true, but there's nothing to stop you using ladders of diodes to produce much softer clipping characteristics that simulate other clipping/crossover behaviours. You could even use passive filters to separate and clip different frequency ranges by different amounts. The world is your oyster really.

*EDIT: I managed to find it I think. It's just a pair of schottky diodes connected across a guitar output. It's simplistic, and you have to be simplistic since the guitar signal peaks at only a couple hundred millivolts -barely enough to induce clipping. Results can be disappointing. But with pro audio you have much larger voltage swings to play with, so you can have fancy ladders of diodes. You can also build in a transformer to boost the voltage, of course.

 

[ruffrecords]

Hey all,

Thank you very much for these insights.

I wondered about the diode clipper but, though I’ve never heard one, people seem pretty critcal of the resulting sonics, a la Black Ice. Is there a method or component choice which is decidedly more pro/useful sounding? Maybe I’ll try it out and see what I hear.

Depends  how you do it. Classic VU meters have a germanium (or other type) bridge rectifier that introduces non-linear distortion. (At Neve we always ensured VU meters were switched away from outputs when measuring distortion). Lots of 50s/60s gear had VU meters across outputs so perhaps that explains some of their 'sound'.

Small core like a Beyer peanut, for example? I have some of those that I could play with. Thing is, and forgive me if you’re well aware, you can turn knobs on the box and it takes the signal from a little harmonically saturated to full on warm distortion. I’m wondering how one can alter the headroom or distortion characteristics of a transformer (small core or otherwise) with a circuit... Or are you all suggesting that the only elements of this which noticeable add distortion are diode clippers?

Easy to arrange different amounts of signal being fed to the transformer and also easy to blend its output with the original so it sounds musical rather than yukky.

Fun stuff. So does this literally mean it could not be fixed by the manufacturer? I’m not 100% on the effects of potted, but I remember you saying something about not being able to replace caps in a Fat Box DI.

It was often done as a means of protecting a design from pirates. Especially attractive if you are a small company and cannot afford patent protection and/or the costs of litigation. Unkind folk might suggest it was also a means of hiding an overhyped, overpriced product which was internally quite simple/cheap.

Cheers

Ian

 

[PRR]

> Classic VU meters have a germanium (or other type) bridge rectifier

VU is copper-oxide.

Germanium was not yet production grade when the precursors of VU were developed.

Copper oxide has even lower "threshold" with a long leaky tail which will detect very small AC.

Copper oxide was in wide use at the time even for power loads. Production is an arcane art but does not need clean-rooms or high-tech.

 

[Audio1Man]

Hi All
You may want to review the presentation the Steve Hogan gave @ Hollywood Sapphire about the “The Ins and Outs of Audio Transformers”. I can’t attach the file as it is 1M in Power point and 5M in PDF.
Email [email protected] and I will send it to you.

 

[pucho812]

Hello Duke,

If you can send an e-mail to Ethan, we can convert the file to be much smaller and have it hosted.

 

[warpie]

Hello Duke,

If you can send an e-mail to Ethan, we can convert the file to be much smaller and have it hosted.

Yes please!

 

[boji]

Here's the external link to pdf:
http://www.hollywoodsapphiregroup.com/insandouts.pdf

 

[abbey road d enfer]

If you add a DC supply, you could use that to DC bias the core by passing DC through a winding and provide even order distortion.

Is that necessary in a tape emulation box?

Anyway it can be done more simply with a diode.

 

[abbey road d enfer]

Or are you all suggesting that the only elements of this which noticeable add distortion are diode clippers?

I would think a primary with multiple taps would provide variable saturation.

 

[ruffrecords]

Here's the external link to pdf:
http://www.hollywoodsapphiregroup.com/insandouts.pdf

If you want greater depth here is a link to Bill Whitlock's chapter on audio transformers from the Handbook for Sound Engineers.

http://jensen-transformers.com/wp-content/uploads/2014/09/Audio-Transformers-Chapter.pdf

Cheers

Ian

 

[illacov]

Hi.

Thanks
-L.

 

[mr coffee]

wouldn't biasing a core with dc as Monte suggested need to be driven with a constant current?

mr coffee